misc/nstat.c

   1 /*
   2  * nstat.c      handy utility to read counters /proc/net/netstat and snmp
   3  *
   4  *              This program is free software; you can redistribute it and/or
   5  *              modify it under the terms of the GNU General Public License
   6  *              as published by the Free Software Foundation; either version
   7  *              2 of the License, or (at your option) any later version.
   8  *
   9  * Authors:     Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
  10  */
  11
  12 #include <stdio.h>
  13 #include <stdlib.h>
  14 #include <unistd.h>
  15 #include <fcntl.h>
  16 #include <string.h>
  17 #include <errno.h>
  18 #include <time.h>
  19 #include <sys/time.h>
  20 #include <fnmatch.h>
  21 #include <sys/file.h>
  22 #include <sys/socket.h>
  23 #include <sys/un.h>
  24 #include <sys/poll.h>
  25 #include <sys/wait.h>
  26 #include <sys/stat.h>
  27 #include <signal.h>
  28 #include <math.h>
  29 #include <getopt.h>
  30
  31 #include <json_writer.h>
  32 #include "version.h"
  33 #include "utils.h"
  34
  35 int dump_zeros;
  36 int reset_history;
  37 int ignore_history;
  38 int no_output;
  39 int json_output;
  40 int no_update;
  41 int scan_interval;
  42 int time_constant;
  43 double W;
  44 char **patterns;
  45 int npatterns;
  46
  47 char info_source[128];
  48 int source_mismatch;
  49
  50 static int generic_proc_open(const char *env, char *name)
  51 {
  52         char store[128];
  53         char *p = getenv(env);
  54
  55         if (!p) {
  56                 p = getenv("PROC_ROOT") ? : "/proc";
  57                 snprintf(store, sizeof(store)-1, "%s/%s", p, name);
  58                 p = store;
  59         }
  60         return open(p, O_RDONLY);
  61 }
  62
  63 static int net_netstat_open(void)
  64 {
  65         return generic_proc_open("PROC_NET_NETSTAT", "net/netstat");
  66 }
  67
  68 static int net_snmp_open(void)
  69 {
  70         return generic_proc_open("PROC_NET_SNMP", "net/snmp");
  71 }
  72
  73 static int net_snmp6_open(void)
  74 {
  75         return generic_proc_open("PROC_NET_SNMP6", "net/snmp6");
  76 }
  77
  78 static int net_sctp_snmp_open(void)
  79 {
  80         return generic_proc_open("PROC_NET_SCTP_SNMP", "net/sctp/snmp");
  81 }
  82
  83 struct nstat_ent {
  84         struct nstat_ent *next;
  85         char             *id;
  86         unsigned long long val;
  87         double             rate;
  88 };
  89
  90 struct nstat_ent *kern_db;
  91 struct nstat_ent *hist_db;
  92
  93 static const char *useless_numbers[] = {
  94         "IpForwarding", "IpDefaultTTL",
  95         "TcpRtoAlgorithm", "TcpRtoMin", "TcpRtoMax",
  96         "TcpMaxConn", "TcpCurrEstab"
  97 };
  98
  99 static int useless_number(const char *id)
 100 {
 101         int i;
 102
 103         for (i = 0; i < ARRAY_SIZE(useless_numbers); i++)
 104                 if (strcmp(id, useless_numbers[i]) == 0)
 105                         return 1;
 106         return 0;
 107 }
 108
 109 static int match(const char *id)
 110 {
 111         int i;
 112
 113         if (npatterns == 0)
 114                 return 1;
 115
 116         for (i = 0; i < npatterns; i++) {
 117                 if (!fnmatch(patterns[i], id, FNM_CASEFOLD))
 118                         return 1;
 119         }
 120         return 0;
 121 }
 122
 123 static void load_good_table(FILE *fp)
 124 {
 125         char buf[4096];
 126         struct nstat_ent *db = NULL;
 127         struct nstat_ent *n;
 128
 129         while (fgets(buf, sizeof(buf), fp) != NULL) {
 130                 int nr;
 131                 unsigned long long val;
 132                 double rate;
 133                 char idbuf[sizeof(buf)];
 134
 135                 if (buf[0] == '#') {
 136                         buf[strlen(buf)-1] = 0;
 137                         if (info_source[0] && strcmp(info_source, buf+1))
 138                                 source_mismatch = 1;
 139                         strlcpy(info_source, buf + 1, sizeof(info_source));
 140                         continue;
 141                 }
 142                 /* idbuf is as big as buf, so this is safe */
 143                 nr = sscanf(buf, "%s%llu%lg", idbuf, &val, &rate);
 144                 if (nr < 2) {
 145                         fprintf(stderr, "%s:%d: error parsing history file\n",
 146                                 __FILE__, __LINE__);
 147                         exit(-2);
 148                 }
 149                 if (nr < 3)
 150                         rate = 0;
 151                 if (useless_number(idbuf))
 152                         continue;
 153                 if ((n = malloc(sizeof(*n))) == NULL) {
 154                         perror("nstat: malloc");
 155                         exit(-1);
 156                 }
 157                 n->id = strdup(idbuf);
 158                 n->val = val;
 159                 n->rate = rate;
 160                 n->next = db;
 161                 db = n;
 162         }
 163
 164         while (db) {
 165                 n = db;
 166                 db = db->next;
 167                 n->next = kern_db;
 168                 kern_db = n;
 169         }
 170 }
 171
 172 static int count_spaces(const char *line)
 173 {
 174         int count = 0;
 175         char c;
 176
 177         while ((c = *line++) != 0)
 178                 count += c == ' ' || c == '\n';
 179         return count;
 180 }
 181
 182 static void load_ugly_table(FILE *fp)
 183 {
 184         char *buf = NULL;
 185         size_t buflen = 0;
 186         ssize_t nread;
 187         struct nstat_ent *db = NULL;
 188         struct nstat_ent *n;
 189
 190         while ((nread = getline(&buf, &buflen, fp)) != -1) {
 191                 char idbuf[4096];
 192                 int  off;
 193                 char *p;
 194                 int count1, count2, skip = 0;
 195
 196                 p = strchr(buf, ':');
 197                 if (!p) {
 198                         fprintf(stderr, "%s:%d: error parsing history file\n",
 199                                 __FILE__, __LINE__);
 200                         exit(-2);
 201                 }
 202                 count1 = count_spaces(buf);
 203                 *p = 0;
 204                 idbuf[0] = 0;
 205                 strncat(idbuf, buf, sizeof(idbuf) - 1);
 206                 off = p - buf;
 207                 p += 2;
 208
 209                 while (*p) {
 210                         char *next;
 211
 212                         if ((next = strchr(p, ' ')) != NULL)
 213                                 *next++ = 0;
 214                         else if ((next = strchr(p, '\n')) != NULL)
 215                                 *next++ = 0;
 216                         if (off < sizeof(idbuf)) {
 217                                 idbuf[off] = 0;
 218                                 strncat(idbuf, p, sizeof(idbuf) - off - 1);
 219                         }
 220                         n = malloc(sizeof(*n));
 221                         if (!n) {
 222                                 perror("nstat: malloc");
 223                                 exit(-1);
 224                         }
 225                         n->id = strdup(idbuf);
 226                         n->rate = 0;
 227                         n->next = db;
 228                         db = n;
 229                         p = next;
 230                 }
 231                 n = db;
 232                 nread = getline(&buf, &buflen, fp);
 233                 if (nread == -1) {
 234                         fprintf(stderr, "%s:%d: error parsing history file\n",
 235                                 __FILE__, __LINE__);
 236                         exit(-2);
 237                 }
 238                 count2 = count_spaces(buf);
 239                 if (count2 > count1)
 240                         skip = count2 - count1;
 241                 do {
 242                         p = strrchr(buf, ' ');
 243                         if (!p) {
 244                                 fprintf(stderr, "%s:%d: error parsing history file\n",
 245                                         __FILE__, __LINE__);
 246                                 exit(-2);
 247                         }
 248                         *p = 0;
 249                         if (sscanf(p+1, "%llu", &n->val) != 1) {
 250                                 fprintf(stderr, "%s:%d: error parsing history file\n",
 251                                         __FILE__, __LINE__);
 252                                 exit(-2);
 253                         }
 254                         /* Trick to skip "dummy" trailing ICMP MIB in 2.4 */
 255                         if (skip)
 256                                 skip--;
 257                         else
 258                                 n = n->next;
 259                 } while (p > buf + off + 2);
 260         }
 261         free(buf);
 262
 263         while (db) {
 264                 n = db;
 265                 db = db->next;
 266                 if (useless_number(n->id)) {
 267                         free(n->id);
 268                         free(n);
 269                 } else {
 270                         n->next = kern_db;
 271                         kern_db = n;
 272                 }
 273         }
 274 }
 275
 276 static void load_sctp_snmp(void)
 277 {
 278         FILE *fp = fdopen(net_sctp_snmp_open(), "r");
 279
 280         if (fp) {
 281                 load_good_table(fp);
 282                 fclose(fp);
 283         }
 284 }
 285
 286 static void load_snmp(void)
 287 {
 288         FILE *fp = fdopen(net_snmp_open(), "r");
 289
 290         if (fp) {
 291                 load_ugly_table(fp);
 292                 fclose(fp);
 293         }
 294 }
 295
 296 static void load_snmp6(void)
 297 {
 298         FILE *fp = fdopen(net_snmp6_open(), "r");
 299
 300         if (fp) {
 301                 load_good_table(fp);
 302                 fclose(fp);
 303         }
 304 }
 305
 306 static void load_netstat(void)
 307 {
 308         FILE *fp = fdopen(net_netstat_open(), "r");
 309
 310         if (fp) {
 311                 load_ugly_table(fp);
 312                 fclose(fp);
 313         }
 314 }
 315
 316
 317 static void dump_kern_db(FILE *fp, int to_hist)
 318 {
 319         json_writer_t *jw = json_output ? jsonw_new(fp) : NULL;
 320         struct nstat_ent *n, *h;
 321
 322         h = hist_db;
 323         if (jw) {
 324                 jsonw_start_object(jw);
 325                 jsonw_pretty(jw, pretty);
 326                 jsonw_name(jw, info_source);
 327                 jsonw_start_object(jw);
 328         } else
 329                 fprintf(fp, "#%s\n", info_source);
 330
 331         for (n = kern_db; n; n = n->next) {
 332                 unsigned long long val = n->val;
 333
 334                 if (!dump_zeros && !val && !n->rate)
 335                         continue;
 336                 if (!match(n->id)) {
 337                         struct nstat_ent *h1;
 338
 339                         if (!to_hist)
 340                                 continue;
 341                         for (h1 = h; h1; h1 = h1->next) {
 342                                 if (strcmp(h1->id, n->id) == 0) {
 343                                         val = h1->val;
 344                                         h = h1->next;
 345                                         break;
 346                                 }
 347                         }
 348                 }
 349
 350                 if (jw)
 351                         jsonw_uint_field(jw, n->id, val);
 352                 else
 353                         fprintf(fp, "%-32s%-16llu%6.1f\n", n->id, val, n->rate);
 354         }
 355
 356         if (jw) {
 357                 jsonw_end_object(jw);
 358
 359                 jsonw_end_object(jw);
 360                 jsonw_destroy(&jw);
 361         }
 362 }
 363
 364 static void dump_incr_db(FILE *fp)
 365 {
 366         json_writer_t *jw = json_output ? jsonw_new(fp) : NULL;
 367         struct nstat_ent *n, *h;
 368
 369         h = hist_db;
 370         if (jw) {
 371                 jsonw_start_object(jw);
 372                 jsonw_pretty(jw, pretty);
 373                 jsonw_name(jw, info_source);
 374                 jsonw_start_object(jw);
 375         } else
 376                 fprintf(fp, "#%s\n", info_source);
 377
 378         for (n = kern_db; n; n = n->next) {
 379                 int ovfl = 0;
 380                 unsigned long long val = n->val;
 381                 struct nstat_ent *h1;
 382
 383                 for (h1 = h; h1; h1 = h1->next) {
 384                         if (strcmp(h1->id, n->id) == 0) {
 385                                 if (val < h1->val) {
 386                                         ovfl = 1;
 387                                         val = h1->val;
 388                                 }
 389                                 val -= h1->val;
 390                                 h = h1->next;
 391                                 break;
 392                         }
 393                 }
 394                 if (!dump_zeros && !val && !n->rate)
 395                         continue;
 396                 if (!match(n->id))
 397                         continue;
 398
 399                 if (jw)
 400                         jsonw_uint_field(jw, n->id, val);
 401                 else
 402                         fprintf(fp, "%-32s%-16llu%6.1f%s\n", n->id, val,
 403                                 n->rate, ovfl?" (overflow)":"");
 404         }
 405
 406         if (jw) {
 407                 jsonw_end_object(jw);
 408
 409                 jsonw_end_object(jw);
 410                 jsonw_destroy(&jw);
 411         }
 412 }
 413
 414 static int children;
 415
 416 static void sigchild(int signo)
 417 {
 418 }
 419
 420 static void update_db(int interval)
 421 {
 422         struct nstat_ent *n, *h;
 423
 424         n = kern_db;
 425         kern_db = NULL;
 426
 427         load_netstat();
 428         load_snmp6();
 429         load_snmp();
 430         load_sctp_snmp();
 431
 432         h = kern_db;
 433         kern_db = n;
 434
 435         for (n = kern_db; n; n = n->next) {
 436                 struct nstat_ent *h1;
 437
 438                 for (h1 = h; h1; h1 = h1->next) {
 439                         if (strcmp(h1->id, n->id) == 0) {
 440                                 double sample;
 441                                 unsigned long long incr = h1->val - n->val;
 442
 443                                 n->val = h1->val;
 444                                 sample = (double)incr * 1000.0 / interval;
 445                                 if (interval >= scan_interval) {
 446                                         n->rate += W*(sample-n->rate);
 447                                 } else if (interval >= 1000) {
 448                                         if (interval >= time_constant) {
 449                                                 n->rate = sample;
 450                                         } else {
 451                                                 double w = W*(double)interval/scan_interval;
 452
 453                                                 n->rate += w*(sample-n->rate);
 454                                         }
 455                                 }
 456
 457                                 while (h != h1) {
 458                                         struct nstat_ent *tmp = h;
 459
 460                                         h = h->next;
 461                                         free(tmp->id);
 462                                         free(tmp);
 463                                 };
 464                                 h = h1->next;
 465                                 free(h1->id);
 466                                 free(h1);
 467                                 break;
 468                         }
 469                 }
 470         }
 471 }
 472
 473 #define T_DIFF(a, b) (((a).tv_sec-(b).tv_sec)*1000 + ((a).tv_usec-(b).tv_usec)/1000)
 474
 475
 476 static void server_loop(int fd)
 477 {
 478         struct timeval snaptime = { 0 };
 479         struct pollfd p;
 480
 481         p.fd = fd;
 482         p.events = p.revents = POLLIN;
 483
 484         sprintf(info_source, "%d.%lu sampling_interval=%d time_const=%d",
 485                 getpid(), (unsigned long)random(), scan_interval/1000, time_constant/1000);
 486
 487         load_netstat();
 488         load_snmp6();
 489         load_snmp();
 490         load_sctp_snmp();
 491
 492         for (;;) {
 493                 int status;
 494                 time_t tdiff;
 495                 struct timeval now;
 496
 497                 gettimeofday(&now, NULL);
 498                 tdiff = T_DIFF(now, snaptime);
 499                 if (tdiff >= scan_interval) {
 500                         update_db(tdiff);
 501                         snaptime = now;
 502                         tdiff = 0;
 503                 }
 504                 if (poll(&p, 1, scan_interval - tdiff) > 0
 505                     && (p.revents&POLLIN)) {
 506                         int clnt = accept(fd, NULL, NULL);
 507
 508                         if (clnt >= 0) {
 509                                 pid_t pid;
 510
 511                                 if (children >= 5) {
 512                                         close(clnt);
 513                                 } else if ((pid = fork()) != 0) {
 514                                         if (pid > 0)
 515                                                 children++;
 516                                         close(clnt);
 517                                 } else {
 518                                         FILE *fp = fdopen(clnt, "w");
 519
 520                                         if (fp)
 521                                                 dump_kern_db(fp, 0);
 522                                         exit(0);
 523                                 }
 524                         }
 525                 }
 526                 while (children && waitpid(-1, &status, WNOHANG) > 0)
 527                         children--;
 528         }
 529 }
 530
 531 static int verify_forging(int fd)
 532 {
 533         struct ucred cred;
 534         socklen_t olen = sizeof(cred);
 535
 536         if (getsockopt(fd, SOL_SOCKET, SO_PEERCRED, (void *)&cred, &olen) ||
 537             olen < sizeof(cred))
 538                 return -1;
 539         if (cred.uid == getuid() || cred.uid == 0)
 540                 return 0;
 541         return -1;
 542 }
 543
 544 static void usage(void) __attribute__((noreturn));
 545
 546 static void usage(void)
 547 {
 548         fprintf(stderr,
 549                 "Usage: nstat [OPTION] [ PATTERN [ PATTERN ] ]\n"
 550                 "   -h, --help          this message\n"
 551                 "   -a, --ignore        ignore history\n"
 552                 "   -d, --scan=SECS     sample every statistics every SECS\n"
 553                 "   -j, --json          format output in JSON\n"
 554                 "   -n, --nooutput      do history only\n"
 555                 "   -p, --pretty        pretty print\n"
 556                 "   -r, --reset         reset history\n"
 557                 "   -s, --noupdate      don't update history\n"
 558                 "   -t, --interval=SECS report average over the last SECS\n"
 559                 "   -V, --version       output version information\n"
 560                 "   -z, --zeros         show entries with zero activity\n");
 561         exit(-1);
 562 }
 563
 564 static const struct option longopts[] = {
 565         { "help", 0, 0, 'h' },
 566         { "ignore",  0,  0, 'a' },
 567         { "scan", 1, 0, 'd'},
 568         { "nooutput", 0, 0, 'n' },
 569         { "json", 0, 0, 'j' },
 570         { "reset", 0, 0, 'r' },
 571         { "noupdate", 0, 0, 's' },
 572         { "pretty", 0, 0, 'p' },
 573         { "interval", 1, 0, 't' },
 574         { "version", 0, 0, 'V' },
 575         { "zeros", 0, 0, 'z' },
 576         { 0 }
 577 };
 578
 579 int main(int argc, char *argv[])
 580 {
 581         char *hist_name;
 582         struct sockaddr_un sun;
 583         FILE *hist_fp = NULL;
 584         int ch;
 585         int fd;
 586
 587         while ((ch = getopt_long(argc, argv, "h?vVzrnasd:t:jp",
 588                                  longopts, NULL)) != EOF) {
 589                 switch (ch) {
 590                 case 'z':
 591                         dump_zeros = 1;
 592                         break;
 593                 case 'r':
 594                         reset_history = 1;
 595                         break;
 596                 case 'a':
 597                         ignore_history = 1;
 598                         break;
 599                 case 's':
 600                         no_update = 1;
 601                         break;
 602                 case 'n':
 603                         no_output = 1;
 604                         break;
 605                 case 'd':
 606                         scan_interval = 1000*atoi(optarg);
 607                         break;
 608                 case 't':
 609                         if (sscanf(optarg, "%d", &time_constant) != 1 ||
 610                             time_constant <= 0) {
 611                                 fprintf(stderr, "nstat: invalid time constant divisor\n");
 612                                 exit(-1);
 613                         }
 614                         break;
 615                 case 'j':
 616                         json_output = 1;
 617                         break;
 618                 case 'p':
 619                         pretty = 1;
 620                         break;
 621                 case 'v':
 622                 case 'V':
 623                         printf("nstat utility, iproute2-%s\n", version);
 624                         exit(0);
 625                 case 'h':
 626                 case '?':
 627                 default:
 628                         usage();
 629                 }
 630         }
 631
 632         argc -= optind;
 633         argv += optind;
 634
 635         sun.sun_family = AF_UNIX;
 636         sun.sun_path[0] = 0;
 637         sprintf(sun.sun_path+1, "nstat%d", getuid());
 638
 639         if (scan_interval > 0) {
 640                 if (time_constant == 0)
 641                         time_constant = 60;
 642                 time_constant *= 1000;
 643                 W = 1 - 1/exp(log(10)*(double)scan_interval/time_constant);
 644                 if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
 645                         perror("nstat: socket");
 646                         exit(-1);
 647                 }
 648                 if (bind(fd, (struct sockaddr *)&sun, 2+1+strlen(sun.sun_path+1)) < 0) {
 649                         perror("nstat: bind");
 650                         exit(-1);
 651                 }
 652                 if (listen(fd, 5) < 0) {
 653                         perror("nstat: listen");
 654                         exit(-1);
 655                 }
 656                 if (daemon(0, 0)) {
 657                         perror("nstat: daemon");
 658                         exit(-1);
 659                 }
 660                 signal(SIGPIPE, SIG_IGN);
 661                 signal(SIGCHLD, sigchild);
 662                 server_loop(fd);
 663                 exit(0);
 664         }
 665
 666         patterns = argv;
 667         npatterns = argc;
 668
 669         if ((hist_name = getenv("NSTAT_HISTORY")) == NULL) {
 670                 hist_name = malloc(128);
 671                 sprintf(hist_name, "/tmp/.nstat.u%d", getuid());
 672         }
 673
 674         if (reset_history)
 675                 unlink(hist_name);
 676
 677         if (!ignore_history || !no_update) {
 678                 struct stat stb;
 679
 680                 fd = open(hist_name, O_RDWR|O_CREAT|O_NOFOLLOW, 0600);
 681                 if (fd < 0) {
 682                         perror("nstat: open history file");
 683                         exit(-1);
 684                 }
 685                 if ((hist_fp = fdopen(fd, "r+")) == NULL) {
 686                         perror("nstat: fdopen history file");
 687                         exit(-1);
 688                 }
 689                 if (flock(fileno(hist_fp), LOCK_EX)) {
 690                         perror("nstat: flock history file");
 691                         exit(-1);
 692                 }
 693                 if (fstat(fileno(hist_fp), &stb) != 0) {
 694                         perror("nstat: fstat history file");
 695                         exit(-1);
 696                 }
 697                 if (stb.st_nlink != 1 || stb.st_uid != getuid()) {
 698                         fprintf(stderr, "nstat: something is so wrong with history file, that I prefer not to proceed.\n");
 699                         exit(-1);
 700                 }
 701                 if (!ignore_history) {
 702                         FILE *tfp;
 703                         long uptime = -1;
 704
 705                         if ((tfp = fopen("/proc/uptime", "r")) != NULL) {
 706                                 if (fscanf(tfp, "%ld", &uptime) != 1)
 707                                         uptime = -1;
 708                                 fclose(tfp);
 709                         }
 710                         if (uptime >= 0 && time(NULL) >= stb.st_mtime+uptime) {
 711                                 fprintf(stderr, "nstat: history is aged out, resetting\n");
 712                                 if (ftruncate(fileno(hist_fp), 0) < 0)
 713                                         perror("nstat: ftruncate");
 714                         }
 715                 }
 716
 717                 load_good_table(hist_fp);
 718
 719                 hist_db = kern_db;
 720                 kern_db = NULL;
 721         }
 722
 723         if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) >= 0 &&
 724             (connect(fd, (struct sockaddr *)&sun, 2+1+strlen(sun.sun_path+1)) == 0
 725              || (strcpy(sun.sun_path+1, "nstat0"),
 726                  connect(fd, (struct sockaddr *)&sun, 2+1+strlen(sun.sun_path+1)) == 0))
 727             && verify_forging(fd) == 0) {
 728                 FILE *sfp = fdopen(fd, "r");
 729
 730                 if (!sfp) {
 731                         fprintf(stderr, "nstat: fdopen failed: %s\n",
 732                                 strerror(errno));
 733                         close(fd);
 734                 } else {
 735                         load_good_table(sfp);
 736                         if (hist_db && source_mismatch) {
 737                                 fprintf(stderr, "nstat: history is stale, ignoring it.\n");
 738                                 hist_db = NULL;
 739                         }
 740                         fclose(sfp);
 741                 }
 742         } else {
 743                 if (fd >= 0)
 744                         close(fd);
 745                 if (hist_db && info_source[0] && strcmp(info_source, "kernel")) {
 746                         fprintf(stderr, "nstat: history is stale, ignoring it.\n");
 747                         hist_db = NULL;
 748                         info_source[0] = 0;
 749                 }
 750                 load_netstat();
 751                 load_snmp6();
 752                 load_snmp();
 753                 load_sctp_snmp();
 754                 if (info_source[0] == 0)
 755                         strcpy(info_source, "kernel");
 756         }
 757
 758         if (!no_output) {
 759                 if (ignore_history || hist_db == NULL)
 760                         dump_kern_db(stdout, 0);
 761                 else
 762                         dump_incr_db(stdout);
 763         }
 764         if (!no_update) {
 765                 if (ftruncate(fileno(hist_fp), 0) < 0)
 766                         perror("nstat: ftruncate");
 767                 rewind(hist_fp);
 768
 769                 json_output = 0;
 770                 dump_kern_db(hist_fp, 1);
 771                 fclose(hist_fp);
 772         }
 773         exit(0);
 774 }